Pakistani security forces have fired into the air and lobbed tear gas in Islamabad, where protesters are holding an early morning march and calling on the country's political leaders to resign and dissolve the government.

The demonstrators gathered on one of the city's main thoroughfares for an anti-corruption protest. They were acting at the urging of populist Pakistani cleric Tahir-ul Qadri. He told the tens of thousands of people at the protest to march on parliament.

Qadri's supporters pushed aside barriers of barbed wire and shipping containers that police had erected to contain the crowd.

The influential cleric said he would speak to his supporters around mid-day outside parliament to press his demand for the government's abdication.

Pakistan is due to hold parliamentary elections in mid-May, and parliament would be dissolved about two months beforehand. But Qadri said the government should step down immediately, to clear the way for an interim Cabinet to root out graft and mismanagement, which he blames for chronic energy shortages, slow economic growth and a rise in crime and Taliban insurgency.

Qadri's black, chauffeur-driven SUV was showered with rose petals by supporters as he arrived at the protest rally.

The Sufi cleric, who runs an educational and religious organization with global reach, recently returned to Pakistan after years living in Canada, where he also has citizenship.

He promised to bring a million demonstrators to the streets of Islamabad, but turnout appeared to fall far short of that goal. Pakistan's interior minister estimated Monday evening that the total crowd would not exceed 25,000.

Still, Qadri was greeted by raucous cheers from supporters as he arrived.

This protest comes just after a three-day demonstration by Hazara Shi'ites in Quetta, capital of southwestern Baluchistan province, protesting against one of the worst sectarian attacks in the country's history – bomb attacks last week that killed nearly 100 people.

After thousands of Shi'ites sat in the roads, refusing to bury their dead, the federal government yielded to the protesters' key demand and dismissed the provincial government.